For more information about OLE, see Chapter 11, "Working with OLE Embedded and OLE Linked Objects."
In many cases, the interface of an object or application can be expressed using a single primary window with a set of supplemental secondary windows. The desktop and taskbar provide management of primary windows. Opening a window puts it at the top of the Z order and places an entry on the taskbar, making it easier for users to switch between windows without having to shuffle or reposition them.
By supporting a single instance model where you activate an existing window (within the same desktop) if the user reopens the object, you make single primary windows more manageable, and reduce the potential confusion for the user. This also provides a data-centered, one-to-one relationship between an object and its window.
In addition, Microsoft OLE supports the creation of compound documents or other types of information containers. Using these constructs, the user can assemble a set of different types of objects for a specific purpose within a single primary window, eliminating the necessity of displaying or editing information in separate windows.
Note
For more information about OLE, see Chapter 11, "Working with OLE Embedded and OLE Linked Objects."
Some types of objects, such as device objects, may not even require a primary window and use only a secondary window for viewing and editing their properties. When this occurs, do not include the Open command in the menu for the object; instead, replace it with a Properties command, defined as the object's default command.
It is also possible for an object to have no windows; an icon is its sole representation. In this very rare case, make certain that you provide an adequate set of menu commands to allow a user to control its activity.